During a barium enema exam, air may be pumped into the colon. The air expands the colon and improves the quality of images. This is called an air-contrast (double-contrast) barium enema. Before a barium enema, your doctor will instruct you to completely empty your colon.
Best Answer: First one is the Upper Oesophageal Sphincter, which allows entry of a food bolus into the oesophagus. Then the Lower Oesophageal Sphincter (also known as cardia, or cardiac sphincter), found at the entrance to the stomach. This stops reflux of food back up the oesophagus. Next is the pyloric sphincter, which allows stomach contents into the duodenum (small intestine) for further digestion. Then the ilio-caecal valve, which isn't a sphincter, but mediates movement of small intestine contents into the large intestine (caecum). There are two sphincters around the anus, the external sphincter and the internal sphincter.
Another important function of stomach acid is the effect that it has on the Lower Esophageal Sphincter (LES). The LES is the valve which allows food to enter the stomach but prohibits reflux of gastric acid into the esophagus. The autonomic nervous system activates the LES in response to increased stomach acidity.